kbx:sqlite: Don't call dotlock_release.

* kbx/backend-sqlite.c (create_or_open_database): Remove call to
dotlock_release, as dotlock_destroy cares the lock if any.

Simply calling dotlock_release was wrong when considering the possible
database_lock==NULL. The check with dotlock_is_locked was added to
avoid warning when not locked, but dotlock_release is not needed here.

• Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>